The present invention relates to a panel for shielding the passage of electromagnetic radio frequency radiation interference therethrough.
The problem of such interference has been on a rapid increase due to the proliferation of electronic equipment such as computers and the like that emit such radiation, particularly in the 500 KH.sub.Z to 1 GH.sub.Z region. The Federal Communications Commission has issued regulations limiting such radiation emissions to the environment to low levels, which therefore requires adequate shielding of such radiation interference emitting electronic equipment in most instances. Most such shielding is now formed by applying relatively thick coats of nickel-acrylic paints over the appropriate substrate. A zinc arc spray treatment of substrates is also somewhat effective. The nickel-acrylic methods are most prevalent in the field because of low initial capital investment with relatively good shielding effectiveness, while having good mechanical and thermal properties at a thickness of 2 to 3 mils. The primary disadvantage of the nickel-acrylic coating is that the deposition thickness depends on the skill of the individual spray operator and quality control can be a problem. If the coating is too thick cracking and delamination occur, and if it is too thin inadequate shielding results. Moreover, the coating process is labor intensive and has relatively high material cost.
There are also some "in-plastic" techniques whereby fillers such as: aluminum flake and/or powder, stainless steel fibers, carbon flake and/or powder, carbon mat, and, more recently, conductive polymeric materials; are incorporated within the interior of the plastic substrate. The widely used "on-plastic" techniques include application of nickel, copper and silver paints, zinc arc sprayed layers, ion plated layers, electro and electrolessly deposited nickel and copper, and vacuum deposited (thermally) layers.
The panel of this invention overcomes the deficiencies with the prior art techniques. The panel of the present invention is a panel of high durability, effectiveness, and low cost. Existing vacuum metalizing equipment can be modified at relatively low cost to slow-discharge treat in situ the surface of the substrate to be coated, followed by successive vapor deposition of the three distinct layers to form the durable shielding composite coating.